Optical inspection of stator slots

ABSTRACT

A system for inspecting a stator stack includes a rotary table, an imaging device configured to take a plurality of images of a portion of the stator stack including a stator slot, an illuminator configured to apply illumination through the stator slot, and an alignment and monitoring system configured to monitor and orient the stator slot relative to the imaging axis. The alignment and monitoring system includes a tilting system configured to move the stator slot between a plurality of orientations relative to an imaging axis, the imaging device configured to take a respective image at each of the plurality of orientations, a controller configured to control the tilting system based on one or more measurements of each image, and a processor configured to analyze each image and select an orientation of the stator slot as an optimal orientation for inspection of the stator slot.

INTRODUCTION

The subject disclosure relates to inspection of electric motor stators,and more particularly to optical inspection of stator slots.

Electric motors are used in a variety of contexts and industries.Electric motors are utilized in the automotive industry, for example, aspart of electric and hybrid vehicles. During manufacturing processes,electric motor components are typically inspected to identify defectsthat could compromise the effectiveness of the finished motors. Forexample, stators making up part of a motor are constructed fromindividual laminations that make up a lamination stack. Defects canarise during construction, examples of which include burrs and geometricvariations due to misalignment of laminations. It is desirable to have asystem and method for inspection of stators during and/or afterconstruction in order to identify and address any defects that couldarise.

SUMMARY

In one exemplary embodiment, a system for inspecting a stator stackincludes a rotary table including a table surface configured to supportthe stator stack, an imaging device configured to take a plurality ofimages of a portion of the stator stack, the portion of the stator stackincluding a stator slot, the imaging device having an imaging axis thatis aligned relative to a surface of the stator stack. The system alsoincludes an illuminator configured to apply illumination through thestator slot, and an alignment and monitoring system configured tomonitor and orient the stator slot relative to the imaging axis. Thealignment and monitoring system includes a tilting system configured tomove the stator slot between a plurality of orientations relative to theimaging axis, the imaging device configured to take a respective imageat each of the plurality of orientations, a controller configured tocontrol the tilting system based on one or more measurements of eachimage, and a processor configured to analyze each image and select anorientation of the stator slot as an optimal orientation for inspectionof the stator slot.

In addition to one or more of the features described herein, the imagingdevice includes an optical camera and a telecentric lens.

In addition to one or more of the features described herein, theprocessor is configured to analyze each image by taking one or moreimage attribute measurements related to an amount of illuminationthrough the stator slot.

In addition to one or more of the features described herein, the optimalorientation is associated with an image having a peak amount ofillumination.

In addition to one or more of the features described herein, theprocessor is configured to measure a depth and a width of the statorslot based on each image.

In addition to one or more of the features described herein, the tiltingsystem includes a pivot, a first lift platform and a second liftplatform configured to be linearly moved in a direction that is normalto the rotary table surface.

In addition to one or more of the features described herein, the firstlift platform is configured to tilt the rotary table along a firstdirection and the second lift platform is configured to tilt the rotarytable along a second direction perpendicular to the first direction.

In addition to one or more of the features described herein, the tiltingsystem includes a base structure supported by the pivot, the first liftplatform and the second lift platform, the first lift platform and thesecond lift platform disposed orthogonally with respect to a location ofthe pivot.

In one exemplary embodiment, a method of inspecting a stator stackincludes disposing the stator stack on a surface of a rotary table of aninspection system, the inspection system including an imaging devicehaving an imaging axis that is aligned relative to a surface of thestator stack, and an illuminator configured to apply illuminationthrough a stator slot. The method also includes taking, by an imagingdevice, a plurality of images of a portion of the stator stack, theportion of the stator stack including the stator slot, the plurality ofimages including a respective image taken at each of a plurality oforientations relative to the imaging axis, the inspection systemincluding a tilting system configured to move the stator slot to each ofthe plurality of orientations, analyzing each image, and selecting anorientation of the stator slot as an optimal orientation based on theanalyzing.

In addition to one or more of the features described herein, theanalyzing includes taking one or more image attribute measurementsrelated to an amount of illumination through the stator slot.

In addition to one or more of the features described herein, the optimalorientation is associated with an image having a peak amount ofillumination.

In addition to one or more of the features described herein, the methodfurther includes measuring a depth and a width of the stator slot basedon each image.

In addition to one or more of the features described herein, the tiltingsystem includes a pivot, a first lift platform and a second liftplatform configured to be linearly moved in a direction that is normalto the rotary table surface, the first lift platform configured to tiltthe rotary table along a first direction and the second lift platformconfigured to tilt the rotary table along a second directionperpendicular to the first direction.

In addition to one or more of the features described herein, the tiltingsystem includes a base structure supported by the pivot, the first liftplatform and the second lift platform, the first lift platform and thesecond lift platform disposed orthogonally with respect to a location ofthe pivot.

In one exemplary embodiment, a method of calibrating a stator stackinspection system includes disposing a reference object including areference stator slot on a rotary table of the inspection system, theinspection system including an imaging device having an imaging axisthat is normal to a surface of the stator stack, an illuminatorconfigured to apply illumination through the reference stator slot, anda tilting assembly. The method also includes acquiring an image of thereference stator slot, inspecting an image attribute along a directionthat extends between a first edge and a second edge of the stator slot,determining a first image attribute gradient corresponding to the firstedge and a second image attribute gradient corresponding to the secondedge, comparing the first image attribute gradient to the second imageattribute gradient, and aligning the imaging device and the illuminatorrelative to a rotary table surface based on the comparing.

In addition to one or more of the features described herein, the firstimage attribute gradient and the second image attribute gradientcorrespond to local maxima of the image attribute.

In addition to one or more of the features described herein, the methodfurther includes estimating a difference between the first imageattribute gradient and the second image attribute gradient, andcomparing the difference to a threshold difference.

In addition to one or more of the features described herein, the methodfurther includes adjusting an alignment of the imaging device and theilluminator based on the difference being greater than or equal to thethreshold difference, taking another image at the adjusted alignment,and estimating the difference for the another image.

In addition to one or more of the features described herein, theadjusting and estimating the difference is performed successively foreach of a plurality of alignments until an optimal alignment is found.

In addition to one or more of the features described herein, the optimalalignment is an alignment associated with an image corresponding to anestimated difference that is less than the threshold.

The above features and advantages, and other features and advantages ofthe disclosure are readily apparent from the following detaileddescription when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only,in the following detailed description, the detailed descriptionreferring to the drawings in which:

FIG. 1 depicts an example of components of a stator including a statorstack;

FIG. 2 depicts the stator stack of FIG. 1 ;

FIG. 3 illustrates an example of dimensions of a stator slot;

FIG. 4 depicts an inspection and monitoring system for opticallyinspecting stator slots, in accordance with an exemplary embodiment;

FIG. 5 depicts an inspection and monitoring system for opticallyinspecting stator slots, in accordance with an exemplary embodiment;

FIG. 6 depicts a tilting system controllable to adjust an orientation ofa stator slot, in accordance with an exemplary embodiment;

FIG. 7 is a flow diagram depicting aspects of a method of inspecting astator slot and stator stack, in accordance with an exemplaryembodiment;

FIG. 8 is an example of an image of a stator slot and an initialcoordinate system;

FIG. 9 depicts aspects of an edge detection method or process, inaccordance with an exemplary embodiment;

FIG. 10 depicts an example of a coordinate system used for measuring animage of a stator slot;

FIG. 11 depicts an example of an image of a stator slot, and illustratesaspects of measuring a stator slot in the image;

FIG. 12 depicts the image of FIG. 11 , and illustrates aspects ofinspecting an edge of the stator slot and identifying one or moredeviations, in accordance with an exemplary embodiment;

FIG. 13 depicts the image of FIG. 11 , and illustrates aspects ofinspecting an edge of the stator slot and identifying one or moredeviations, in accordance with an exemplary embodiment;

FIG. 14 depicts a state machine used to perform aspects of the method ofFIG. 7 , in accordance with an exemplary embodiment;

FIG. 15 depicts a calculator, in accordance with an exemplaryembodiment;

FIGS. 16A and 16B depict a reference stator slot and an image thereof,used in performing a calibration method, in accordance with an exemplaryembodiment;

FIGS. 17A-F depict examples of images of the stator slot of FIGS. 16Aand 16B, and illustrate examples of the calibration method; and

FIG. 18 depicts a computer system in accordance with an exemplaryembodiment.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, its application or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

In accordance with one or more exemplary embodiments, methods, devicesand systems are provided for inspecting stators and stator components.In an embodiment, the methods, devices and systems are configured tomeasure stator slot dimensions and inspect stators and stator componentsfor deviations, such as geometric discontinuities and burrs. A“deviation” refers to any feature of a stator slot that deviates from adesired geometry, desired alignment or other desired configuration ofthe stator slot. Examples of deviations include burrs and other defects.

An embodiment of an inspection system includes a rotary table having atable surface configured to support a stator stack, an imaging assemblyfor taking images of individual stator slots of the stator stack, and anilluminator for applying illumination through a stator slot when thestator slot is imaged. For example, the imaging assembly is an opticalcamera having an imaging axis in a direction that is generally normal tothe rotary table surface, so that images of each stator slot are takenfrom above. The illuminator applies illumination from under the statorstack through a slot during imaging.

When taking images, it is desirable to properly align the camera and theilluminator (or optics connected thereto) so that the imaging axis andthe illumination axis align and are normal to the stator stack.Embodiments include calibration methods for determining the properalignment of the imaging assembly and the illuminator with respect toone another and the rotary table surface (and/or a surface of the statorstack).

The inspection system also includes an alignment and monitoring systemhaving a tilting assembly and a controller. The tilting assembly iscontrollable to adjust the orientation of the stator slot being imaged.In an embodiment, the tilting assembly includes a support structuremounted on a pivot (e.g., a ball joint) and two orthogonally arrangedlift platforms. Each lift platform is linearly moveable so that therotary table and stator stack can be moved according to six independentcoordinates.

Embodiments also include methods for controlling the imaging assembly,illuminator and tilting assembly, and for inspecting stator slots tomeasure dimensions and detect deviations and defects. An embodiment of amethod includes rotationally positioning the stator stack to place astator slot in the camera’s field of view, and taking a series of imagesat each of a plurality of orientations. Each image is analyzed toestimate an amount of light through the stator slot, and to estimatedimensions of the stator slot. An optimal orientation is selected fromthe different orientations based on the analysis. An “optimalorientation” is an orientation that permits the most amount of light topass through the stator slot and/or provides for the most accuratemeasurements. Images at the optimal orientation are analyzed to measuredimensions and inspect the stator slot. The method is repeated for eachselected stator slot in the stator stack.

Embodiments described herein present numerous advantages and technicaleffects. The embodiments provide for a non-contact inspection systemthat is able to quickly and efficiently inspect stator stacks, forexample, during a stator and/or motor manufacturing process. Theembodiments allow for quick inspection of stator slot dimensions, andautomatic alignment of each individual slot to ensure that images aretaken under optimal conditions. In this way, defects or deviations canbe readily detected and addressed.

FIGS. 1 and 2 depict an example of a stator assembly 10, which includesa stator stack 12 formed by a plurality of laminations. The laminationsmay be produced via a stamping process. Stator windings 14 (e.g., heavygage bar magnet wires) are wound through stator slots 16 in the statorstack 12. An insulator such as phase paper 18 is included within thestator slots 16, for example, by inserting the paper 18 into each statorslot 16 prior to inserting the windings 14.

The dimensional tolerance between the stator slots 16 and the windings14 is tight, resulting in very small clearances. Undesirable features(generally referred to herein as “deviations”), such as burrs andgeometric discontinuities (e.g., due to misalignment of thelaminations), can negatively affect the clearance and can cause damage,failure and/or sub-optimal performance. For example, deviations cancause damage to the paper 18 and/or wire coatings, resulting in partialdischarge and/or motor failure. Geometric deviations or discontinuitiescan affect a motor’s electric and thermal performance (e.g., electricaldeterioration of motor performance or potential Corona effects).

Embodiments provide an effective technique for measuring geometricalfeatures of stator slots at various stages of manufacture. Theembodiments are capable of quickly identifying defects, and can beeffectively employed in large volume production processes. There arenumerous challenges inherent in inspection of stator stacks, includingdifficulties in measuring slot dimensions and identifying possibleburrs, particularly when it is desired to perform inspections under timeconstraints due to the speed of a manufacturing process. The embodimentsdescribed herein address such challenges and present significantimprovements in inspection, manufacturing and quality control.

FIG. 3 shows a portion of the stator stack 12 and a close up view of astator slot 16, and illustrates an example of geometric featuresthereof. As shown, the stator slot 16 is defined by adjacent teeth 15,and has a depth d extending between short edges 17 a and 17 b. Thestator slot 16 also has central longitudinal axis C, and a width wbetween a first long edge 19 a and an opposing long edge 19 b. The widthw may be variable (e.g., the width w is greater near the teeth 15).

FIGS. 4 and 5 depict embodiments of an inspection system 20, whichincludes an imaging assembly 21. It is noted that various embodimentsare discussed in conjunction with a coordinate system defined byorthogonal x-, y- and z-axes for illustration purposes.

The imaging assembly 21 has an imaging device 22, such as an opticalcamera, configured to acquire images of the stator slots 16 via atelecentric lens 24. The images are taken from above the stator stack12, such that the imaging axis is at least substantially orthogonal toan x-y plane defined by the x-axis and the z-axis. The x-y plane maycorrespond to a surface of a rotary table 36 when in a default levelposition.

An illumination assembly 26 includes an illuminator 28 (e.g., atelecentric illuminator) and a mirror 30 configured to directillumination from below the stator stack 12 and through the stator slot16 being imaged. The illuminator 28 has an illumination axis that ispreferably aligned with the imaging axis (i.e., parallel to andcoincident with the imaging axis). The imaging device 22 may be mountedon a rail 34, and the illuminator 28 may be mounted on a rail 32, toallow for lateral adjustment (e.g., along a direction parallel to thex-y plane).

FIG. 4 depicts an embodiment in which the imaging device 22 and theilluminator 28 are arranged in parallel with each other and with the x-yplane. A mirror 35 is included as part of the imaging assembly 21, sothat the imaging device 22 can acquire top-down images. FIG. 5 depictsan embodiment in which the imaging device 22 is arranged orthogonal tothe illuminator 28, and the mirror 35 is excluded.

As shown in FIG. 4 , the imaging device 22 may be connected to aprocessing unit 37. The processing unit 37 may be configured to performvarious functions, such as receiving and analyzing images, controllingoperation and position of the imaging assembly 21 and the illuminationassembly 26, and operating a tilting system 40 discussed below.

The stator stack 12 can be mounted on a support structure that includesa platform 38 and a rotary table 36 that is controlled to rotate thestator stack 12 about the z-axis so that each desired stator slot 16 canbe imaged by the imaging device 22.

Referring to FIG. 6 , in an embodiment, the support structure and thestator stack 12 are supported by a kinematic tilting system 40. Thetilting system 40 includes a base structure 42 (also referred to as abase 42) mounted on a pivot 44 (e.g., a ball joint) and supported by twolift platforms 46 and 48 so that the base 42 can be tilted as desired.Each lift platform is moveable vertically (along the z-axis) usinglinear stepper motors or other suitable actuators. The lift platforms 46and 48 are arranged orthogonally with respect to the location of thepivot 44. The tilting system 40 allows the position and orientation ofthe stator stack 12 (or stator slot 16) to be defined in terms of sixindependent coordinates, including three translations (e.g., in the x, yand z directions) and three rotations (e.g., about the y-axis, about thex-axis and about the z-axis).

In this embodiment, a first lift platform 46 (also referred to as an“alpha lift”) is configured to tilt the base 42 so that the base 42rotates along the x-axis. In other words, the first lift platform 46causes the base 42 to rotate and define a first angle θ₁ between thex-axis and the z-axis (where an angle of zero degrees indicates that thebase 42 is level with respect to the x-axis). The first lift platform 46may be used in conjunction with the imaging assembly 21 to measure adepth d of a stator slot as discussed further herein.

The second lift platform 48 (also referred to as a “beta lift”) isconfigured to tilt the base 42 so that the base 42 rotates along they-axis. The second lift platform 48 causes the base 42 to rotate anddefine a second angle θ₂ between the y-axis and the z-axis (where anangle of zero degrees indicates that the base 42 is level with respectto the y-axis). The second lift platform 48 may be used with the imagingassembly 21 to measure a width w of a stator slot as discussed furtherherein.

The kinematic tilting system 40 and the imaging system 20 may be used toimage or inspect components of the stator stack 12. In an embodiment,the imaging device 22 is used to successively image each stator slot 16(or selected slots 16), by taking images of a given slot and thenrotating the stator stack 12 to locate an adjacent slot 16 or other slot16 under the imaging device 22. For each stator slot 16, the stator slot16 is oriented via the tilting system 40 to maximize the view into thestator slot 16 and allow for a full view of the stator slot edges. Forexample, the stator slot 16 is first oriented relative to the x-axis byactuating the alpha lift 46, and one or more first images of the statorslot 16 are taken. Additional images are taken as the alpha lift 46 isat different vertical positions, and the images are used to determineoptimal alignment (e.g., optimal angle θ₁). The images may also be usedto measure short edges of the stator slot 16 and the depth d (e.g., byanalyzing an image taken at the optimal alignment or optimal angle θ₁).

The stator slot 16 is then oriented relative to the y-axis by actuatingthe beta lift 48, optionally after returning the alpha lift 46 to adefault position (e.g., angle θ₁ is zero). One or more second images ofthe stator slot 16 are taken at a first beta lift position. Additionalimages are taken when the beta lift 48 is at different verticalpositions. One or more images are analyzed to inspect long edges of theslot 16 and measure width, and/or determine optimal alignment (e.g.,optimal angle θ₂). For example, an image taken at the optimal alignmentor optimal angle θ₂ is analyzed to measure and/or inspect the longedges. In addition, one or more images of the long edges may beinspected to identify any defects or deviations, such as burrs.

It is noted that although embodiments are described herein in thecontext of stator slots, they are not so limited and can be used toimage any desired component, object or surface.

FIG. 7 illustrates an embodiment of a method 60 of inspecting a statorstack 12 and stator slots 16. Aspects of the method 60 may be performedby a processor or processors, such as the processing unit 37 (alone orin conjunction with other processors, such as a tilting assemblycontroller). It is noted the method 60 may be performed by any suitableprocessing device or system, or combination of processing devices. Themethod 60 is discussed in conjunction with the stator stack 12 and thetilting system 40, but is not so limited, as the method 60 may beperformed on other components or objects, and the method 60 may beperformed using any device or system capable of changing orientations asdiscussed herein.

The method 60 includes a number of steps or stages represented by blocks61-69. The method 60 is not limited to the number or order of stepstherein, as some steps represented by blocks 61-69 may be performed in adifferent order than that described below, or fewer than all of thesteps may be performed.

At block 61, the inspection system 20 is initially calibrated to ensurethat the imaging assembly 21 and the illuminator 28 are properlyaligned. In an embodiment, the inspection system 20 is properlycalibrated when the imaging axis, the illumination axis and a lengthaxis (perpendicular to an imaged surface) are parallel.

In an embodiment, the imaging assembly 21 and the illumination assembly26 are calibrated by acquiring an image of a reference slot in areference artifact, or acquiring an image of a reference slot in each ofa plurality of reference artifacts. Each artifact is an object (e.g., areference block) having a reference slot. The artifacts are imaged usingthe imaging assembly 21 and analyzed to determine whether the imagingdevice 22 and the telecentric lens 24 are properly aligned with theilluminator 28. For example, one artifact represents a narrow portion ofa stator slot 16 (a portion between ends of adjacent teeth) and anotherartifact represents a wide portion of a stator slot 16 (a portionextending radially outwardly from the portion). Edge detection isperformed on an image of the narrow portion to detect opposing edges,and a gradient profile of one edge is compared with a gradient profileof an opposing edge. The profiles are compared to determine a similaritytherebetween. If the profiles are sufficiently similar (e.g., within aselected gradient difference), the narrow portion is properly aligned.Edge detection and comparison is similarly performed on the wideportion. If the wide and/or narrow portion is not properly aligned, theimaging device 22 is adjusted and the above artifact analysis procedureis repeated.

In an embodiment, the imaging assembly 21 is calibrated by acquiring animage of a reference slot in each of a plurality of reference artifacts.Each artifact is an object (e.g., a reference block) having a referenceslot. The artifacts are imaged using the imaging assembly 21 andanalyzed to determine whether the imaging device 22 and the telecentriclens 24 are properly aligned with the illuminator 28. For example, oneartifact is a reference block having a first thickness, which includes arepresentative stator slot. Another artifact is a reference blockincluding a representative stator slot, and having a second thicknessthat is different than the first thickness. Images of each referenceblock are taken, and the dimensions of the reference slots are measuredin the images. If the measured dimensions are within a thresholddifference from actual dimensions of the reference slots, the imagingassembly is properly aligned.

At block 62, the stator stack 12 is mounted on the rotary table 36, andthe stator slots 16 in the camera view are observed. At block 63, therotary table 36 and/or the stator stack 12 is rotated so that thecurrent slot 16 (i.e., slot to be imaged) is in an angular position withrespect to the edges of the image and with respect to the x and y-axes.This prevents aliasing phenomena from occurring.

At block 64, a coordinate system is defined for the stator slot 16. Inan embodiment, the coordinate system is defined by specifying an initialcoordinate system, detecting one or more edges of a slot 16, androtating or translating to a new coordinate system based on theorientation of the edge(s).

FIG. 8 depicts an example of an image 70 of stator slots 16 as viewed bythe camera. An initial coordinate system is defined, for example, ashaving an x-axis and a y-axis that are aligned with sides or boundariesof the image 70.

Edge detection is performed to detect a long edge 72 of the slot 16 anda short edge 74, and the edges are used to define a new coordinatesystem. FIG. 9 shows an example of aspects of an edge detection processfor detecting the short edge 74.

As shown in FIG. 9 , a rectangular search area or region of interest(ROI) 76 is defined, which includes a plurality of parallel lines alongwhich a search is performed for a gradient (e.g., a gradient above athreshold value) in an image attribute (e.g., brightness, contrast, grayscale, etc.) or pixel value. Pixels at which the gradient exceeds athreshold are used to define the short edge 74.

Once the short edge and long edge orientations are determined, a newcoordinate system is defined based on the edge orientations. Forexample, as shown in FIG. 10 , a new coordinate system is defined havingan x′-axis parallel to a long edge 72 (or parallel to the central axisC) and a y′-axis parallel to a short edge 74.

Referring again to FIG. 7 , at block 65, a width measurement and defectidentification process is performed to determine a width of the statorslot 16, and to identify any burrs, defects or other deviations alongthe width of the slot (and along the long edges 72).

In an embodiment, the width measurement and defect identificationprocess includes taking images of the slot 16 at each of a plurality oforientations. The orientations are achieved, in an embodiment, byactuating the beta lift 48 so that the stator stack 12 is oriented atdifferent values of the angle θ₂. At each orientation, an image isacquired, and the acquired images are analyzed as discussed furtherherein to determine an optimal angle θ₂ and to measure the width.Measurements of width w may be taken using an acquired image or imagescorresponding to the optimal angle θ₂. The beta lift 48 may be returnedto a default position after the width measurements are complete. Thewidth measurements may be performed when the alpha lift 46 is maintainedat a default position, but the method 60 is not so limited.

At block 66, a depth measurement and defect identification process issimilarly performed to determine dimensions including depth d of thestator slot 16, and to identify any deviations (e.g., burrs) along theshort edges 74. The process includes actuating the alpha lift 46 toorient the stator stack 12 at multiple orientations, and taking an imageof the stator slot 16 at each orientation. An acquired image for eachorientation is analyzed as discussed further herein to determine anoptimal angle θ₁ and measure the depth. Measurements of depth d may betaken using an acquired image or images corresponding to the optimalangle θ₁. The depth measurements may be performed when the beta lift 48is maintained at a default position, but the method 60 is not solimited.

At block 67, it is determined whether there are additional stator slots16 to be measured. If so, at block 68, the stator stack 12 is rotated sothat the next adjacent stator slot 16 (or other selected slot 16) iscentered in the camera view and the steps at blocks 65 and 66 arerepeated.

When all of the selected stator slots 16 have been measured, the resultsmay be displayed to a user (e.g., engineer or technician) and/or anotherprocessing device or storage location, at block 69.

Various actions may be taken if there is a defect or deviation, or ifdimensions of a slot are incorrect. For example, the stator stack 12 maybe removed from a manufacturing process, or a manufacturing process maybe adjusted to correct any errors. Slots having identified burrs can beaddressed by shearing, smoothing or otherwise shaping the slots.

In an embodiment, images are analyzed to determine a proper orientationby measuring image attributes that are related to an amount of lightthat is transmitted through a stator slot 16 when imaged. For example,the brightness of a portion of an image through the slot 16 is measuredand compared to the other images of the slot 16 to determine which imagehas the most amount of light through the slot (i.e., a peak brightness).Images corresponding to different orientations may be successivelyacquired and analyzed until the peak brightness is found.

The width w of a stator slot 16 in an image is measured using anysuitable image analysis technique. In an embodiment, the width ismeasured by calculating an average width based on determining multipledistances between the long edges 72 (e.g., distances at the ends of thelong edges 72). A distance (e.g., along the y′-axis) may be defined by aset of opposing points (i.e., a distance between a point on a long edge72 and a point on an opposing long edge 72). The points may be selectedfrom each long edge 72 as detected or selected from a best fit linegenerated for each long edge 72.

The width measurement can be performed at each orientation, or performedonly on the image corresponding to the peak brightness. For example, asshown in FIG. 11 , best fit lines 80 and 82 are determined (e.g., via arake function) for each long edge 72, and the width w is calculated atmultiple locations.

FIG. 12 illustrates aspects of an embodiment of an inspection method fordetecting burrs and other deviations along the long edges 72. The methodincludes determining the best fit line 80, and calculating a distance pbetween an edge contour and the best fit line 80 at multiple locationsalong the edge 72. A maximum distance pmax represents the extent of apotential burr or deviation. A minimum width of the slot 16 may becalculated by subtracting the maximum distance pmax from the width w (oraverage width). Although FIG. 12 only shows inspection of one long edge72, it is understood that the other long edge is similarly inspected.

The depth d of a stator slot 16 in an image can be measured using anysuitable image analysis technique. In an embodiment, the depth ismeasured by calculating an average depth based on determining a distancebetween the short edges 74. For example, as shown in FIG. 13 , a depth d(along the x′-axis) is calculated on either side of a stator tooth. Anedge 74a is detected, and a first distance is calculated between theedge 74a and the opposing edge 74 (or between best fit lines). A seconddistance is similarly calculated between the edge 74b and the opposingedge 74, and an average depth is calculated.

An embodiment of a measurement and inspection method is discussed withreference to FIG. 14 . The various method steps or stages are performedvia a state machine 90 that directs a processing device to control thetilting system 40, control image acquisition, perform variouscalculations and measurements, and store measurements (e.g., asvariables) and other data. It is noted that the method is not limited touse with a state machine, as the steps or stages can be performed usinganother type of algorithm.

Each of the states in the state machine 90 has a default transition witha default dependency condition. One or more of the states can be changedto transition to user-selected parameters.

The method starts and the tilting system 40 is in a default position. Inthe default position, the rotary table 36 is level (i.e., orthogonal tothe imaging axis) and the inspection system 20 is in a reset state 92.For example, the state machine 90 causes the alpha lift 46 and the betalift 48 to be adjusted by actuating their respective stepper motorsuntil proximity sensors at each lift are triggered. The alpha and betalifts may then be moved at the same increments to put the system at adesired default position.

Adjustment of the alpha and beta lifts may be performed in motor steps,also referred to as increments. Each increment is a defined distancealong the z-axis. However, embodiments described herein are not solimited, as the lifts can be adjusted using any suitable actuator oradjustment technique.

The state machine 90 transitions to a “measure b” state 94, in which aninitial image is taken at the default orientation and width measurementsare performed. In an embodiment, the beta lift 48 is then moved in anegative or downward direction, so that the beta lift 48 can be movedupward in increments through various positions as subsequent images aretaken.

The initial image is analyzed to determine an amount of light thatpasses through the imaged stator slot 16. The amount of light may bedetermined by pixel count (i.e., the number of pixels in the image thatmeet (e.g., are greater than or equal to, or less than or equal to) aselected image attribute threshold). For example, the initial image isanalyzed to determine the number of pixels that meet or exceed aselected brightness value. In another example, the pixel count is anumber of pixels that have a gray scale value that is less than or equalto a selected gray scale value threshold. The highest pixel count at agiven point in the method is referred to as a peak pixel count or peakillumination.

The state machine 90 transitions to a “jog beta” state 96, at which thebeta lift 48 is moved to another position (e.g., is incremented upward),and then transitions back to the measure b state 94 and an image isacquired at the position. The state machine transitions 90 between thesestates (taking images at successive positions) until an image having apeak pixel count or peak measurement is found.

It is noted that the width w (e.g., an average width) may be measured ineach image, and the edges many be inspected or analyzed for detection ofdeviations. Measurement data may be stored via a “data log” state 98.

Once the peak pixel count is found, the position of the beta lift 48 islogged as the peak or best beta lift position, and the state machine 90transitions to an “adjust b” state 100, in which the beta lift 48 ismoved back to the default position.

The state machine 90 transitions to a “prepare a” state 102, in whichthe alpha lift 46 is moved downward to an initial position by a selectednumber of increments. At a “measure a” state 104, an initial image istaken at the initial orientation and depth d measurements are performed.The initial image is analyzed to determine an amount of light thatpasses through the slot 16, for example, by calculating a pixel countcorresponding to the number of pixels that meet a selected imageattribute threshold.

The state machine 90 transitions to a “jog alpha” state 106, at whichthe alpha lift 46 is moved to another position (e.g., is incrementedupward) and then back to the measure a state 104, at which in image istaken. The state machine 90 transitions between these states until animage having a peak pixel count is found. The depth d may be measured ineach image, and the short edges 74 may be inspected or analyzed fordetection of deviations. Measurement data may be stored via the data logstate 98.

Once the peak pixel count is found, the position of the alpha lift 46 islogged as the peak or best alpha lift position, and the state machine 90transitions to an “adjust a” state 108, in which the alpha lift 46 ismoved back to the default position.

The state machine 90 then transitions to a “slot number” or “slot #”state 110 if additional slots are to be imaged, and the slot number isnoted. The state machine transitions to a “next slot” state 112 and therotary table 38 is rotated to put an adjacent slot in the imagingdevice’s field of view. The adjacent slot is imaged and the lifts arecontrolled as discussed above. If all slots have been imaged, the statemachine transitions to a “last slot” state 114 and the method ends. Insome cases, it is desirable to measure a subset of the slots (e.g.,every sixth slot). If fewer than all of the slots are being imaged, thestate machine can track the slot numbers and skip a slot bytransitioning to a “skip slot” state 116

FIG. 15 depicts an example of a peak width calculator 99 that is used toprovide a running average tabulation to smooth out stray measurements.For each taken image (the “current image”), the calculator 99 comparesimage measurements and analysis results to previously recorded data, anddetermines whether the current image represents a peak measurement(e.g., peak pixel count or peak illumination). In this way, a runningrecord of the peak measurement is maintained.

In the calculator 99, “xsum” represents the peak measurement, and iscalculated based on an average of the first width and the second widthin combination with the pixel count of the peak measurement. Values“burrvar1” and “burrvar2” represent the maximum distance values used toidentify burrs (burrvar1 is a maximum distance between the first longedge and a fitted line, and burrvar2 is a maximum distance between thesecond long edge and fitted line) of the peak measurement. The beta liftposition (beta motor position) associated with the peak measurement is“best”.

For a current measurement, the calculator 99 receives as inputs acalibrated maximum distance value from inspection of the first long edgeas a variable “burr1”, and a calibrated maximum distance value frominspection of the second long edge as a variable “burr2.” The pixelcount representing the amount of illumination is input as variables“pix1” and “pix2.” The variable pix1 represents a raw pixel distance(e.g., measured in number of pixels) between the edges at a locationalong the depth of the stator slot 16. The variable pix2 represents araw pixel distance between the edges at a different location along thedepth of the stator slot 16.

The distance between the long edge best fit lines at one end of thestator slot 16 is input from the current measurement as variable “x1”,and the distance between the lines at a second end is input as variable“x2”. The minimum width is input as “minw”. The motor position “mp” ofthe current measurement is decremented from motor position of the peakmeasurement (“best”). “xavg” is an average width of the slot. A minimumdistance “xmin” may be selected (e.g., to minimum distance betweenadjacent teeth, selected so that wires can be inserted into the slot)

The calculator calculates the average of x1 and x2, denoted “avgvar” andadds the avgvar to the pixel count. The resulting value “xnew”represents the current measurement. xnew is compared to xsum. If xnew isless than or equal to xsum, the existing parameter of xsum is maintainedas an output of the calculator 99. If xnew is greater than xsum, thecalculator 99 outputs the parameters of the current measurement. Forexample, if xnew is greater than xsum, the new best position of the betalift (“newmpmax”) is the current motor position “mp”. Variables “burr1”and “burr2” will be input as inspection variables “burrvar1” and“burrvar2” for the next measurement.

Embodiments also include a method of calibrating the imaging assembly 21and the illuminator 28 to ensure proper alignment with respect to thestator stack 12 and/or rotary table 36. FIGS. 16A and 16B, and FIGS.17A-F depict aspects of an example of the method. The method includestaking measurements of representative slots in at least two referenceobjects, where each reference object has a different dimension (e.g.,thickness). In the method, two or more reference objects are imaged. Forexample, a first reference object is in the form of a relatively thinplate (e.g., steel plate) having a first thickness (e.g., 0.5 mm to 1 mmthick), and includes a first slot with known slot dimensions. A secondreference object is in the form of a relatively thick plate or block(e.g., 100 mm thick) including a second slot having slot dimensions thatare the same as or similar to the first slot. FIG. 16A depicts anexample of a reference object 120 having a thickness in the z-axisdirection of about 100 mm, and having a representative slot 122. FIG.16B depicts an example of an image 124 of the slot 122.

The method includes a measurement process that includes taking one ormore first images of the first reference object using the imaging system20, and performing a first measurement of one or more dimensions (e.g.,width) of the first slot. One or more second images of the secondreference object are taken and a second measurement of one or moredimensions of the second slot is performed. A difference between thefirst measurement and the actual dimensions of the first slot (i.e., afirst difference) is determined and compared to a threshold differencevalue. A difference between the second measurement and the actualdimensions of the second slot (i.e., a second difference) is determinedand compared to the threshold difference value.

For example, measurement of the dimensions includes extracting aplurality of edge points (e.g., 100 points) from an image andcalculating average, maximum, and minimum widths. The thresholddifference in this example is an error of about 1 to 2 percent of theactual slot widths.

If the first difference and the second difference is less than or equalto the threshold, the imaging system 20 is properly aligned.

If the difference is greater than the threshold, the imaging system 20is not properly aligned. The imaging assembly 21 and/or the illuminator28 may be adjusted and the imaging process is repeated. Adjustment andimaging as described herein may be iteratively performed until a properalignment is reached.

In an embodiment, the calibration method includes acquiring a referenceobject such as the reference object 120, which has the stator slot 122formed therein. The reference stator slot 122 has known dimensions andis known to be defect free.

An image of the reference slot 122 is taken by the imaging assembly 21,and the image is analyzed to identify opposing edges. Each edgecorresponds to an image attribute gradient (i.e., a change in value ofthe image attribute along a selected direction). The gradients arecompared, and if the difference between them is below a thresholddifference, the imaging assembly and the illuminator 28 are consideredto be properly aligned. If the difference is greater than the thresholddifference, the imaging assembly orientation, the illuminatororientation, and/or the rotary table orientation are adjusted and theprocess is repeated until a proper or desired alignment is found.

FIGS. 17A-C represent an analysis of an image of a misaligned imagingassembly. FIG. 17A shows an acquired image 130. The image is analyzedalong a search direction (line 132) to generate an edge map 134 and aline profile 136. representing a brightness or gray scale value ofpixels in the image 130. As shown in FIG. 17C, there is a significantdifference between peaks in the line profile 136, indicatingmisalignment.

FIGS. D-F represent an analysis of an image of a properly alignedimaging assembly. FIG. 17D shows an acquired image 170. The image isanalyzed along a search direction (line 172) to generate an edge map 174and a line profile 176. As In this example, as shown in FIG. 17F, thepeaks represent a similar gradient, indicating proper alignment.

FIG. 18 illustrates aspects of an embodiment of a computer system 140that can perform various aspects of embodiments described herein. Thecomputer system 140 includes at least one processing device 142, whichgenerally includes one or more processors for performing aspects ofmethods described herein.

Components of the computer system 140 include the processing device 142(such as one or more processors or processing units), a memory 144, anda bus 146 that couples various system components including the systemmemory 144 to the processing device 142. The system memory 144 mayinclude a variety of computer system readable media. Such media can beany available media that is accessible by the processing device 142, andincludes both volatile and non-volatile media, and removable andnon-removable media.

For example, the system memory 144 includes a non-volatile memory 148such as a hard drive, and may also include a volatile memory 150, suchas random access memory (RAM) and/or cache memory. The computer system140 can further include other removable/non-removable,volatile/non-volatile computer system storage media.

The system memory 144 can include at least one program product having aset (e.g., at least one) of program modules that are configured to carryout functions of the embodiments described herein. For example, thesystem memory 144 stores various program modules that generally carryout the functions and/or methodologies of embodiments described herein.A module or modules 152 may be included to perform functions related toacquiring images and/or controlling scanning speed and operationalparameters. An image analysis module 154 may be included for analysis ofimages as described herein. The system 140 is not so limited, as othermodules may be included. As used herein, the term “module” refers toprocessing circuitry that may include an application specific integratedcircuit (ASIC), an electronic circuit, a processor (shared, dedicated,or group) and memory that executes one or more software or firmwareprograms, a combinational logic circuit, and/or other suitablecomponents that provide the described functionality.

The processing device 142 can also communicate with one or more externaldevices 156 as a keyboard, a pointing device, and/or any devices (e.g.,network card, modem, etc.) that enable the processing device 142 tocommunicate with one or more other computing devices. Communication withvarious devices can occur via Input/Output (I/O) interfaces 164 and 165.

The processing device 142 may also communicate with one or more networks166 such as a local area network (LAN), a general wide area network(WAN), a bus network and/or a public network (e.g., the Internet) via anetwork adapter 168. It should be understood that although not shown,other hardware and/or software components may be used in conjunctionwith the computer system 40. Examples include, but are not limited to:microcode, device drivers, redundant processing units, external diskdrive arrays, RAID systems, and data archival storage systems, etc.

While the above disclosure has been described with reference toexemplary embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from its scope. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the disclosure without departing from the essentialscope thereof. Therefore, it is intended that the present disclosure notbe limited to the particular embodiments disclosed, but will include allembodiments falling within the scope thereof.

What is claimed is:
 1. A system for inspecting a stator stack,comprising: a rotary table including a table surface configured tosupport the stator stack; an imaging device configured to take aplurality of images of a portion of the stator stack, the portion of thestator stack including a stator slot, the imaging device having animaging axis that is aligned relative to a surface of the stator stack;an illuminator configured to apply illumination through the stator slot;and an alignment and monitoring system configured to monitor and orientthe stator slot relative to the imaging axis, the alignment andmonitoring system including: a tilting system configured to move thestator slot between a plurality of orientations relative to the imagingaxis, the imaging device configured to take a respective image at eachof the plurality of orientations; a controller configured to control thetilting system based on one or more measurements of each image; and aprocessor configured to analyze each image and select an orientation ofthe stator slot as an optimal orientation for inspection of the statorslot.
 2. The system of claim 1, wherein the imaging device includes anoptical camera and a telecentric lens.
 3. The system of claim 1, whereinthe processor is configured to analyze each image by taking one or moreimage attribute measurements related to an amount of illuminationthrough the stator slot.
 4. The system of claim 3, wherein the optimalorientation is associated with an image having a peak amount ofillumination.
 5. The system of claim 1, wherein the processor isconfigured to measure a depth and a width of the stator slot based oneach image.
 6. The system of claim 1, wherein the tilting systemincludes a pivot, a first lift platform and a second lift platformconfigured to be linearly moved in a direction that is normal to therotary table surface.
 7. The system of claim 6, wherein the first liftplatform is configured to tilt the rotary table along a first directionand the second lift platform is configured to tilt the rotary tablealong a second direction perpendicular to the first direction.
 8. Thesystem of claim 7, wherein the tilting system includes a base structuresupported by the pivot, the first lift platform and the second liftplatform, the first lift platform and the second lift platform disposedorthogonally with respect to a location of the pivot.
 9. A method ofinspecting a stator stack, comprising: disposing the stator stack on asurface of a rotary table of an inspection system, the inspection systemincluding an imaging device having an imaging axis that is alignedrelative to a surface of the stator stack, and an illuminator configuredto apply illumination through a stator slot; taking, by an imagingdevice, a plurality of images of a portion of the stator stack, theportion of the stator stack including the stator slot, the plurality ofimages including a respective image taken at each of a plurality oforientations relative to the imaging axis, the inspection systemincluding a tilting system configured to move the stator slot to each ofthe plurality of orientations; and analyzing each image, and selectingan orientation of the stator slot as an optimal orientation based on theanalyzing.
 10. The method of claim 9, wherein the analyzing includestaking one or more image attribute measurements related to an amount ofillumination through the stator slot.
 11. The method of claim 10,wherein the optimal orientation is associated with an image having apeak amount of illumination.
 12. The method of claim 9, furthercomprising measuring a depth and a width of the stator slot based oneach image.
 13. The method of claim 9, wherein the tilting systemincludes a pivot, a first lift platform and a second lift platformconfigured to be linearly moved in a direction that is normal to therotary table surface, the first lift platform configured to tilt therotary table along a first direction and the second lift platformconfigured to tilt the rotary table along a second directionperpendicular to the first direction.
 14. The method of claim 13,wherein the tilting system includes a base structure supported by thepivot, the first lift platform and the second lift platform, the firstlift platform and the second lift platform disposed orthogonally withrespect to a location of the pivot.
 15. A method of calibrating a statorstack inspection system, comprising: disposing a reference objectincluding a reference stator slot on a rotary table of the inspectionsystem, the inspection system including an imaging device having animaging axis that is normal to a surface of the stator stack, anilluminator configured to apply illumination through the referencestator slot, and a tilting assembly; acquiring an image of the referencestator slot; inspecting an image attribute along a direction thatextends between a first edge and a second edge of the stator slot;determining a first image attribute gradient corresponding to the firstedge and a second image attribute gradient corresponding to the secondedge; comparing the first image attribute gradient to the second imageattribute gradient; and aligning the imaging device and the illuminatorrelative to a rotary table surface based on the comparing.
 16. Themethod of claim 15, wherein the first image attribute gradient and thesecond image attribute gradient correspond to local maxima of the imageattribute.
 17. The method of claim 15, further comprising estimating adifference between the first image attribute gradient and the secondimage attribute gradient, and comparing the difference to a thresholddifference.
 18. The method of claim 17, further comprising adjusting analignment of the imaging device and the illuminator based on thedifference being greater than or equal to the threshold difference,taking another image at the adjusted alignment, and estimating thedifference for the another image.
 19. The method of claim 18, whereinthe adjusting and estimating the difference is performed successivelyfor each of a plurality of alignments until an optimal alignment isfound.
 20. The method of claim 19, wherein the optimal alignment is analignment associated with an image corresponding to an estimateddifference that is less than the threshold.